We propose a randomized, controlled clinical trial designed to assess the long-term effects of a strict lifestyle-change program on lipids, myocardial perfusion, and coronary atherosclerosis. Fifty patients are randomly assigned to receive either the lifestyle-change program plus usual medical care or to receive only the usual medical care. Endpoint measures include lipids, lipoproteins, apoproteins, quantitative coronary arteriography and cardiac positron emission tomography (PET) at baseline, after one year, and after four years. Lifestyle changes include a low-fat vegetarian diet, smoking cessation, moderate exercise, and stress management training. Lipid-lowering drugs are not used. To date, 17 patients have completed testing at baseline and after one year. In the experimental group, dietary cholesterol had decreased from 215.0 for 2.6 mg/day and total dietary fat has decreased from 70.0 to 15.0 grams/day, whereas dietary changes in the control group have veen substantially less. In the experimental group after one year, there was a 3.84 percent diameter stenosis regression, whereas in the control group there was a 5.69 percent diameter stenosis progression (P = 0.025). Six of the first seven experimental patients demonstrated some overall regression of coronary atherosclerosis, whereas eight of the first ten control patients demonstrated some overall progression of coronary atherosclerosis. In the experimental group there was a 0.27 increase in coronary flow reserve (CFR), whereas the control group showed a 0.43 decrease in CFR (P = 0.025). We propose to study these changes after four years to determine if patients in the experiments group can e motivated to maintain long-term adherence to his lifestyle-change program and to determine if the small degree of atherosclerosis regression detected after one year will continue to increase. Also, we propose or develop further and validate cardiac PET by comparing it to quantitative coronary arteriography and to develop statistical methods appropriate for the analyses of distribution-free randomized cluster experiments.